L.6 Pasteurella

Question 1

What type of organisms does Pasteurella colonise?

Answer 1

Mammals both domestic and feral

This includes both pet and wild animals.

Question 2

What is the normal flora of Pasteurella in cats and dogs?

Answer 2

Normal nasopharyngeal flora

This means that Pasteurella is typically found in the respiratory tract of these animals.

Question 3

How is most human disease associated with Pasteurella contracted?

Answer 3

Zoonotic infection from dog bites or cat scratches

These infections are transmitted from animals to humans.

Question 4

How many species are in the Pasteurella genus?

Answer 4

Six species

These species include various types, with P. multocida being the most significant for human infections.

Question 5

Which species of Pasteurella most commonly infects humans?

Answer 5

P. multocida

This species is frequently isolated from animal bites.

Question 6

What percentage of dog bites and cat scratches are associated with P. multocida?

Answer 6

50% of dog bites and 75% of cat scratches

This indicates a high prevalence of P. multocida in these types of injuries.

Question 7

What are the three syndromes associated with human infection of Pasteurella?

Answer 7

• Skin and soft tissue infections
• Chronic pulmonary disease
• Systemic infection

These syndromes vary based on the patient’s health status and the nature of the infection.

Question 8

What characterizes skin and soft tissue infections caused by Pasteurella?

Answer 8

Localized swelling and cellulitis following dog bite/cat scratch

This typically occurs in the area of the injury.

Question 9

In which patients is chronic pulmonary disease associated with Pasteurella most likely to occur?

Answer 9

Patients with lung dysfunction

These patients may have pre-existing respiratory conditions.

Question 10

What type of host is at risk for systemic infections by Pasteurella?

Answer 10

Immunocompromised host

Individuals with weakened immune systems are more susceptible to severe infections.

Question 11

What are the virulent factors of Pasteurella?

Answer 11

• Capsule
• Endotoxin

These factors help the bacteria evade the immune system and cause disease.

Question 12

What is the first step in lab investigation for Pasteurella infection?

Answer 12

Diagnosis depends on clinical appearance, history of animal contact, and results of culture

A thorough history and physical examination are crucial.

Question 13

What is the clinical specimen used for diagnosing Pasteurella infections?

Answer 13

Pus from skin/tissue infection

This specimen type is essential for culture and identification of the organism.

Question 14

What is the growth requirement for isolating Pasteurella in the lab?

Answer 14

Not fastidious pathogen; grows on blood agar incubated at 37°C in air overnight

This means it can grow in standard lab conditions.

Question 15

What clue indicates that Pasteurella may not grow on MacConkey agar?

Answer 15

Fails to grow on MacConkey

This characteristic helps differentiate Pasteurella from other bacteria.

Question 16

What is the colonial morphology of P. multocida?

Answer 16

Small grey wet colonies

This refers to the appearance of the colonies when cultured on appropriate media.

Question 17

What type of bacteria is P. multocida?

Answer 17

Gram negative coccobacilli

Coccobacilli are short, rod-shaped bacteria.

Question 18

Is P. multocida catalase positive or negative?

Answer 18

Catalase positive

This indicates the presence of the enzyme catalase which breaks down hydrogen peroxide.

Question 19

Is P. multocida oxidase positive or negative?

Answer 19

Oxidase positive

This indicates the presence of cytochrome c oxidase in the bacteria.

Question 20

What biochemical tests confirm the presence of P. multocida?

Answer 20

1. Fermentation of peptone water sugars
2. Indole production
3. Ornithine decarboxylase test

These tests help identify specific metabolic capabilities of the bacteria.

Question 21

What sugars does P. multocida ferment in the peptone water sugars test?

Answer 21

Glucose and sucrose

The fermentation of these sugars results in a color change indicating acid production.

Question 22

What does the phenol red indicator do in the fermentation test?

Answer 22

Turns yellow due to pH decrease if fermentation occurs

This indicates that acid is produced from sugar fermentation.

Question 23

What is the principle behind the indole production test?

Answer 23

Hydrolysis of tryptophan leads to accumulation of indole

Indole turns cherry red in colour on the surface after adding Kovacs reagent.

Question 24

What color indicates a positive result for indole production?

Answer 24

Cherry red

This color change occurs after the addition of Kovacs reagent.

Question 25

What components are found in the ornithine decarboxylase test medium?

Answer 25

Amino acid of interest, small amount of glucose/dextrose, pH indicator ## Footnote This setup allows for the detection of decarboxylase activity based on pH changes.

Question 26

What happens to the pH indicator when P. multocida ferments glucose/dextrose?

Answer 26

Turns yellow (acidic pH) ## Footnote This indicates acid production from fermentation.

Question 27

What color indicates a positive result for ornithine decarboxylase test?

Answer 27

Purple colour ## Footnote This indicates an alkaline environment due to decarboxylation of the amino acid.

Question 28

What is the byproduct of the decarboxylation of lysine or ornithine?

Answer 28

An amine which is alkaline ## Footnote This byproduct raises the pH of the medium.